EP1933431A1 - Source de lumière laser émettant de la lumière à la surface d'un cristal photonique bidimensionnel - Google Patents

Source de lumière laser émettant de la lumière à la surface d'un cristal photonique bidimensionnel Download PDF

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Publication number
EP1933431A1
EP1933431A1 EP06783175A EP06783175A EP1933431A1 EP 1933431 A1 EP1933431 A1 EP 1933431A1 EP 06783175 A EP06783175 A EP 06783175A EP 06783175 A EP06783175 A EP 06783175A EP 1933431 A1 EP1933431 A1 EP 1933431A1
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Prior art keywords
refractive index
photonic crystal
dimensional photonic
laser light
modified refractive
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EP06783175A
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German (de)
English (en)
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EP1933431A4 (fr
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Susumu Noda
Eiji Miyai
Dai Ohnishi
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Rohm Co Ltd
Kyoto University
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Rohm Co Ltd
Kyoto University
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Priority claimed from JP2005255878A external-priority patent/JP4310297B2/ja
Priority claimed from JP2005374208A external-priority patent/JP4294023B2/ja
Application filed by Rohm Co Ltd, Kyoto University filed Critical Rohm Co Ltd
Publication of EP1933431A1 publication Critical patent/EP1933431A1/fr
Publication of EP1933431A4 publication Critical patent/EP1933431A4/fr
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/11—Comprising a photonic bandgap structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S2301/00—Functional characteristics
    • H01S2301/18—Semiconductor lasers with special structural design for influencing the near- or far-field
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
    • H01S5/042—Electrical excitation ; Circuits therefor
    • H01S5/0425—Electrodes, e.g. characterised by the structure
    • H01S5/04254—Electrodes, e.g. characterised by the structure characterised by the shape
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
    • H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
    • H01S5/18308—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] having a special structure for lateral current or light confinement
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
    • H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
    • H01S5/18358—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] containing spacer layers to adjust the phase of the light wave in the cavity

Definitions

  • the present invention relates to a surface-emitting laser light source for emitting laser light in a direction perpendicular to the surface of a flat light source.
  • laser light sources include a Fabry-Perot laser light source, which uses a Fabry-Perot resonator, and a distributed feedback (DFB) laser light source, which uses a diffraction grating. These types of laser light sources produce an oscillation of laser light by amplifying light of a predetermined wavelength through resonation or diffraction.
  • DFB distributed feedback
  • a photonic crystal includes a dielectric matrix body in which an artificial periodic structure is created.
  • the periodic structure is created by providing the matrix body with a periodic arrangement of areas whose refractive index differs from that of the matrix body (this area is called the "modified refractive index area” hereinafter).
  • the periodic structure causes a Bragg diffraction within the crystal and creates an energy band gap with respect to the energy of light.
  • photonic crystal laser light sources one of which utilizes a band-gap effect to use a point-like defect as a resonator, and the other utilizes a standing wave at a band edge where the group velocity of light becomes zero. Both of them cause an oscillation of laser light by amplifying light of a predetermined wavelength.
  • Patent Document 1 discloses a laser light source in which a two-dimensional photonic crystal is created in the vicinity of an active layer containing a light-emitting material.
  • This two-dimensional photonic crystal is created from a plate-shape matrix body made of a semiconductor in which cylindrical holes are arranged periodically (in a triangular, square, or hexagonal lattice pattern or similar pattern) and the refractive index of the matrix body is periodically distributed over a two-dimensional area. This period is adjusted so that it equals the wavelength within the medium of light generated in the active layer by injecting carriers from the electrode. Therefore, two-dimensional standing waves are created within the two-dimensional photonic crystal, whereby the light is intensified to realize a laser oscillation.
  • Fig. 1 schematically shows standing waves created within the two-dimensional photonic crystal disclosed in Patent Document 1.
  • Fig. 1 shows only a one-dimensional aspect of the standing waves in a specific direction (called the "x-direction" hereinafter) within the crystal surface. If, for example, holes are arranged in a square lattice pattern, another standing wave occurs in the direction perpendicular to the x-direction.
  • the standing wave has two modes: the first mode has a node at the holes 12 of the two-dimensional photonic crystal 11, whereas the second mode has an antinode in the same location.
  • the first mode is anti-symmetric with respect to the z-axis
  • the second mode is symmetric.
  • the distribution function of the plane waves propagating in the z-direction takes a uniform value with respect to the x-direction.
  • the distribution function is an odd function for the anti-symmetric mode or an even function for the symmetric mode.
  • the mode is symmetric, the first-order diffracted light is emitted in the direction perpendicular to the surface because the overlap integral between the symmetric waves and the external plane waves is not zero.
  • the anti-symmetric mode since the overlap integral between the generated waves and the external plane waves is zero, the emission of the first-order diffracted light in the direction perpendicular to the surface does not occur due to the interference.
  • the anti-symmetric mode of light cannot be extracted in the direction perpendicular to the surface.
  • two-dimensional photonic crystals have a finite size. Therefore, even the anti-symmetric mode of light has its symmetry broken, so that the light can be extracted in the direction perpendicular to the surface. However, even in this case, the intensity of light to be extracted in the direction perpendicular to the surface is weakened by receiving the effects of interference.
  • Patent Document 2 discloses a surface-emitting laser light source having a two-dimensional photonic crystal in which the lattice structure has translational symmetry but does not have rotational symmetry so that the symmetry within a plane parallel to the matrix body is broken.
  • this type of symmetric structure can be obtained by arranging holes, which are refractive-index areas, in a square lattice pattern and creating a plane shape (i.e.
  • the lattice structure of a two-dimensional photonic crystal in these laser light sources has a lower degree of symmetry than the lattice structure of Fig. 1 , it is possible to suppress the interference effects of the anti-symmetric mode of light and increase the intensity of light to be extracted in the direction perpendicular to the surface more than conventional intensities of light.
  • a differential quantum efficiency ⁇ d in which the denominator refers to an increased amount of a current injected to a laser light source and the numerator refers to an increased amount of outputted light resulting from the increase of the current in the direction perpendicular to the surface.
  • the differential quantum efficiency ⁇ d is proportional to a value expressed by: ⁇ ⁇ 1 / Q ⁇ 1 / Q ⁇ + 1 / Q ⁇ + ⁇ where Q ⁇ is a Q value in the direction perpendicular to the surface, Q // is a Q value in the side surface direction, and ⁇ is a dimensionless factor indicating internal absorption and scattering loss.
  • Fig. 2 shows a photonic band chart of a two-dimensional photonic crystal in which holes are arranged in a square lattice pattern.
  • the band edges "A" and "B" of the two bands located on a low-energy side (or low-frequency side) contribute to the laser oscillation.
  • the band edge "B” exhibits a flat dispersion relation in the vicinity of the ⁇ point, which suggests that more light having a wave number other than the ⁇ point is mixed in the finitely periodic structure of actual use.
  • the present inventors calculated the Q value of the two-dimensional photonic crystal in the surface-emitting laser light source using the two-dimensional phonic crystal disclosed in Patent Document 2, and revealed that the Q ⁇ value for the band edge "B" is as high as approximately several hundred thousands to several millions when the Q ⁇ value for the band edge "A” is set to approximately several thousands by appropriately setting the hole size. If the Q ⁇ value of the band edge "B” with respect to the band edge "A” is such a large value, a laser oscillation may possibly occur in the band edge "B". As explained earlier, the band edge "A” is normally selected in laser light sources actually used; therefore, if the Q ⁇ value of the band edge "B” is large, it may possibly cause an unstable two-mode oscillation. Moreover, if the band edge "B” is selected for an oscillation, the Q ⁇ value is too large and thereby the efficiency of extracting light in the direction perpendicular to the surface is reduced.
  • the surface-emitting laser light source using the two-dimensional photonic crystal disclosed in Patent Document 2 has the following problems when it is manufactured.
  • a matrix body (or a matrix body with a laminated layer such as an activation layer) of the two-dimensional photonic crystal is first fabricated and subjected to dry etching or other processes to periodically create equilateral triangular prism holes in the material body.
  • respective layers (cladding layer and electrode or the like) including the matrix body are piled and heated to be fused together.
  • corners of the equilateral triangular prism of the holes are occasionally deformed into a round shape close to a cylinder. If this deformation occurs, the round plane shape of the holes has a higher degree of symmetry than the equilateral triangular prism, in which the efficiency of extracting light is reduced.
  • One objective of the present invention is to provide a surface-emitting laser light source using a two-dimensional photonic crystal which has a high efficiency for extracting light in the direction perpendicular to the surface and is difficult to receive the effects of deformation caused by heat or other factors, and a manufacturing method thereof.
  • a surface-emitting laser light source using a two-dimensional photonic crystal according to the present invention has been achieved to solve the previously mentioned problems and a first aspect thereof includes:
  • each of the modified refractive index regions may have an obliquely columnar shape whose main axis is tilted to a line perpendicular to the matrix body at 20 to 45 degrees.
  • the modified refractive index regions may be shaped like an obliquely standing equilateral triangular prism which is tilted to the base side of the equilateral triangle of a cross section on the matrix body as advancing from a plane opposite of the active layer toward the active layer.
  • a second aspect of the surface-emitting laser light source using the two-dimensional photonic crystal according to the present invention includes:
  • the modified refractive index regions in the modified refractive index region group may have different plane shapes from one another.
  • Each of the modified refractive index regions in the modified refractive index region group is desirably thicker as the area of the plane shape threreof is larger.
  • the present invention also provides a method for manufacturing the surface-emitting laser source using the two-dimensional photonic crystal according to the aforementioned second aspect of the present invention. Specifically, the present method is:
  • a first aspect of a surface-emitting laser light source using a two-dimensional photonic crystal (referred to as a "laser light source” hereinafter), and a second aspect of a laser light source are now explained in detail.
  • the two-dimensional photonic crystal is provided on one side of the active layer.
  • the two-dimensional photonic crystal does not need to be in direct contact with the active layer; it is possible to place a spacer or other members between them.
  • the active layer may be the same as those conventionally used in Fabry-Perot laser light sources.
  • the two-dimensional photonic crystal is created from a plate-shaped matrix body in which a large number of modified refractive index regions whose refractive index differs from that of the matrix body are periodically arranged. It is possible to create the modified refractive index regions by embedding certain members whose refractive index differs from that of the matrix body into the matrix body, but the modified refractive index regions are desirably created by arranging holes in the matrix body, because this design provides a larger difference in refractive index from that of the matrix body and is easier to manufacture.
  • the first aspect and the second aspect use inventive shapes applied to the modified refractive index regions as described hereafter in order to increase the efficiency of extracting light and make it difficult to receive the effects of deformation caused by heat or other factors.
  • the modified refractive index regions are columnar with a predetermined cross-sectional shape, and the main axis of each of the columnar regions is tilted to the surface of the matrix body.
  • the "columnar” in the present application refers to a three-dimensional shape whose cross sections parallel to the layers is uniform and the line connecting the centers of gravity of the cross sections is a straight line. And this line is called the main axis of the column.
  • the modified refractive index regions having such a shape do not have symmetry within a plane disposed in parallel to the matrix body, or more specifically, do not have rotational symmetry around an axis perpendicular to the matrix body.
  • the emitted light of the anti-symmetric mode is not canceled out even in the central area of the two-dimensional photonic crystal because the modified refractive index region does not have symmetry as stated earlier. Therefore, the efficiency of extracting light in the direction perpendicular to the surface is improved.
  • the first aspect of the laser light source allows suppression of a Q ⁇ B value which is a Q ⁇ value with respect to a band edge "B".
  • the reason is considered as follows. A node of a standing wave created in the photonic crystal and the active layer is disposed in the vicinity of the center of gravity of the modified refractive index region within a plane in parallel to the matrix body. Meanwhile, light has maximum intensity in the active layer, whereby the electric field distribution of light is strongly influenced by the shape of the modified refractive index region which is in the vicinity of a bottom surface closest to the active layer within the photonic crystal.
  • the center of gravity of the bottom surface shape on the active layer side is displaced from a position of the node of the standing wave. Therefore, asymmetrical electric field distribution is created within the bottom surface, where the Q ⁇ value decreases.
  • the position of the node is slightly different between the band edge "A" mode and the band edge "B” mode even if they share the same structure of the two-dimensional photonic crystal.
  • Both the Q ⁇ value and the efficiency of extracting light in the direction perpendicular to the surface are dependent on an angle made by the main axis of a column of each of the modified refractive index regions and the surface of the matrix body, and a sectional shape of the column.
  • the obliquely cylindrical shape refers to a column whose cross section is circular and whose main axis is tilted to the surface of the matrix body.
  • the Q ⁇ A value can be suppressed to achieve approximately several thousands to ten thousands.
  • the Q ⁇ B value is much smaller than the Q ⁇ A value.
  • the obliquely equilateral triangular prism refers to a column whose cross-sectional shape is an equilateral triangle and whose main axis is tilted to the surface of the matrix body.
  • the three-dimensional shape of an obliquely equilateral triangular prism as a whole varies dependent on a tilted direction of the main axis, where a relation between the Q ⁇ A value and the Q ⁇ B value varies.
  • the (i) case has a tendency close to that of the obliquely cylindrical shape, or more specifically, the Q ⁇ A value is about several thousands and the Q ⁇ B value is much lower than the Q ⁇ A value. Accordingly, (i) is more desirable than (ii) in the present invention.
  • the first aspect of the laser light source is capable of maintaining the characteristic shape of the modified refractive index regions in which rotational symmetry is not present around an axis perpendicular to the surface of the matrix body. Therefore, reduction in the efficiency of extracting light can be suppressed even if such deformation occurs.
  • the two-dimensional photonic crystal has a matrix body in which a large number of modified refractive index region groups are periodically arranged.
  • the modified refractive index region group is made of a plurality of elementary modified refractive index regions, and the modified refractive index region groups create periodic refractive index distribution. That is, periodic refractive index distribution of the two-dimensional photonic crystal in the second aspect of the laser light source is created by arranging the modified refractive index region groups on respective lattice points of, for example, a square or triangular lattice.
  • At least two of the plurality of the elementary modified refractive index regions belonging to each of the modified refractive index region groups differs from one another in thickness. As long as this condition is satisfied, every elementary modified refractive index region in a modified refractive index region group may have different thicknesses, or some of the elementary modified refractive index regions may have the same thickness.
  • a thickness in each of the elementary modified refractive index regions is set, the shape of the modified refractive index region group within a cross section in parallel to the matrix body can be changed dependent on a position of the cross section. Therefore, a lower degree of symmetry can be obtained within a plane in parallel to the matrix body, which enables to suppress reduction in the efficiency of extracting laser light caused by cancellation of the anti-symmetric mode resulting from interference.
  • each of the elementary modified refractive index regions in a modified refractive index region group is slightly deformed by a heating process at the time of fabrication, it does not make all of the elementary modified refractive index regions to have the same thickness. Therefore, it is possible to maintain the characteristic shape of the modified refractive index region group, where reduction in the efficiency of extracting light caused by such deformation can be suppressed.
  • each of the elementary modified refractive index regions in a modified refractive index region group may have the same plane shape
  • each of the elementary modified refractive index regions desirably has a different plane shape in order to provide a lower degree of symmetry within the plane.
  • the plane shape of an elementary modified refractive index region in a modified refractive index region group has a larger area as the elementary modified refractive index region is thicker.
  • the two-dimensional photonic crystal is manufactured, in many cases holes are created within the matrix body by using a dry etching method. As the area in the plane shape of a hole to be created is smaller, it is more difficult for an etching gas to penetrate into the hole when the hole is created, which makes the etching speed slower. As a result, each of the holes (or an elementary modified refractive index region) within a modified refractive index region group becomes thicker as the area thereof is larger.
  • the modified refractive index region groups according to the present invention can be easily fabricated without requiring special techniques.
  • the dry etching has to be discontinued before the entire group of holes to be created in the matrix body completely penetrate through the matrix body because penetration of the entire group of holes into the matrix body causes all the modified refractive index regions to have the same thickness.
  • a modified refractive index region group can be made of: a first modified refractive index region having a substantially rectangular plane shape; and a second modified refractive index region which is substantially circular with a diameter shorter than a long side of the first modified refractive index region, having a smaller area and being thinner than the first modified refractive index region.
  • plane shapes of the first modified refractive index region and the second modified refractive index region may be slightly distorted, or corners of the first modified refractive index region of a rectangular shape may be deformed and rounded, as long as the "symmetry-breaking" effect is not impaired.
  • the second modified refractive index region is naturally thinner than the first modified refractive index regions when the first modified refractive index region is set to have an area smaller than that of the second modified refractive index region.
  • the modified refractive index region group including the first modified refractive index region and the second modified refractive index region as previously stated has a plane shape close to a triangle as a whole. That is, the first modified refractive index region constitutes one side of the triangle, whereas the second modified refractive index region constitutes one corner facing that side. It is equivalent to the plane shape of the modified refractive index regions belonging to the two-dimensional photonic crystal for use in the surface-emitting laser disclosed in Patent Document 2.
  • the present invention provides a different thickness between the first modified refractive index region and the second modified refractive index region, a degree of symmetry in the modified refractive index regions (or groups) is made lower than that of the surface-emitting laser light disclosed in Patent Document 2, so that the reduction in the efficiency of extracting laser light caused by cancellation of the anti-symmetric mode resulting from the interference can be suppressed.
  • the characteristic plane shape can be maintained in which a long side of the first modified refractive index region corresponds to one side of the triangle and the second modified refractive index region corresponds to one corner facing the side, in addition to maintaining the aforementioned thickness in each of the modified refractive index regions. Therefore, it is possible to suppress the reduction in the efficiency of extracting light caused by deformation of the modified refractive index regions.
  • a first embodiment of the laser light source according to the present invention one example of the first aspect of the surface-emitting laser light is explained referring to Figs. 3 to 5 .
  • an active layer 23 made of Indium Gallium Arsenide (InGaAs)/Gallium Arsenide (GaAs) and having multiple quantum wells (MQW) is provided between an anode 21 and a cathode 22.
  • a two-dimensional photonic crystal layer 24 made of p-type GaAs is formed on the active layer 23 via a spacer layer 261, which is also made of p-type GaAs.
  • the two-dimensional photonic crystal layer 24 includes a plate member having holes 25 periodically arranged in a square lattice pattern. The shape of the holes 25 is described later.
  • the spacer layer 261 and the two-dimensional photonic crystal layer 24 are integrally created as a single layer, in which the holes 25 are present only in the two-dimensional photonic crystal layer 24 which is on the upper side of the spacer layer 261.
  • a spacer layer 262 made of p-type GaAs, a cladding layer 271 made of p-type AlGaAs and a contact layer 28 made of p-type GaAs are provided between the active layer 23 and the anode 21.
  • a spacer layer 263 made of n-type GaAs and a cladding layer 272 made of n-type AlGaAs are provided between the active layer 23 and the cathode 22.
  • the spacer layer 262 is separated from the two-dimensional photonic crystal layer 24 in order to show the structure of the two-dimensional photonic crystal layer 24.
  • a coordinate system is defined here by setting one direction of the square lattice formed by the holes 25 as an x-axis, the other direction thereof as a y-axis, and a direction perpendicular to the two-dimensional photonic crystal layer 24 as a z-axis.
  • the main axis is tilted to the x-axis.
  • a direction from the active layer 23 toward the two-dimensional photonic crystal layer 24 is also set as a positive direction of the z-axis.
  • Fig. 4 shows a perspective view, a sectional view and projection views for the shape of a single hole 25.
  • Fig. 4(a) is a perspective view
  • Fig. 4(b) is a projection view to the x-z plane
  • Fig. 4(c) is a projection view to the y-z plane
  • Fig. 4(d) is a sectional view (or plan view) on the surface of the two-dimensional photonic crystal layer 24 disposed on the spacer layer 262.
  • a large number of the holes 25 having the same shape are actually arranged in the two-dimensional photonic crystal layer 24 in a square lattice pattern.
  • the two-dimensional photonic crystal layer 24 and the spacer layer 262 are depicted in a transparent form in order to show the shape of the hole 25.
  • the plane shape of the hole 25 on the x-y plane is circular, and this plane shape remains the same in any cross sections disposed in parallel to the surface regardless of the z-values. Since the main axis of the hole 25 is tilted to the x-axis direction, a shape is provided in such a way that this circle moves to the positive direction of the x-axis as the cross section moves to the positive direction of the z-axis. That is, as shown in Figs. 4(a) and 4(b) , an upper portion (or positive direction of the z-axis) of the main axis 31 is tilted to the positive direction of x. It should be noted that the main axis 31 is not tilted to the y-direction as shown in Fig. 4(c) .
  • An operation of the laser light source in the present embodiment is basically similar to that of a conventional surface-emitting laser light source using a two-dimensional photonic crystal.
  • a voltage is applied between the anode 21 and the cathode 22
  • positive holes from the anode 21 and electrons from the anode 22 are injected to the active layer 23 respectively to emit light by the recombination of the positive holes and electrons.
  • This light receives feedback from the two-dimensional photonic crystal layer 24, wbereby a laser oscillation occurs.
  • This laser light is extracted from the contact layer 28 (or the emission surface) to the outside.
  • Fig. 5 shows the calculation results of the Q ⁇ A value and the Q ⁇ B value when ⁇ is 10, 20, 30 and 45 degrees in the laser light source according to the present embodiment. Calculation was made in this situation by a three-dimensional FDTD method for the two-dimensional photonic crystal layer 24 which has an infinitely periodic structure to expand infinitely in the x-y plane, and an 18% ratio of the volume (i.e. filling factor) occupied by the holes 25 in the two-dimensional photonic crystal layer 24. It should be noted that the Q ⁇ A value and the Q ⁇ A value are both infinite when ⁇ is 0 degrees, though it is not shown in Fig. 5 .
  • These calculation results suggest that a laser oscillation by the band edge "A" can be obtained in the laser light source of the present embodiment at least when ⁇ is in the range of 20 to 45 degrees.
  • the laser light sources in these embodiments have a structure similar to that of the laser light source of the first embodiment shown in Fig. 3 with the exception of the shape of the holes.
  • Fig. 6 shows the shape of a hole 45 in the second embodiment
  • Fig. 7 shows the shape of a hole 55 in the third embodiment.
  • (a) is a perspective view
  • (b) is a protection view to the x-z plane
  • (c) is a projection view to the y-z plane
  • (d) is a sectional view (or plan view) on the surface of the two-dimensional photonic crystal layer 24 disposed on the spacer layer 262.
  • a large number of holes having the same shape are actually arranged in a square lattice pattern in the two-dimensional photonic crystal layer 24, though the holes 44 and 45 are shown as a single hole in Figs. 6 and 7 .
  • the plane shape of the holes on the x-y plane is an equilateral triangle as shown in the plan views of Fig. 6(d) and Fig. 7(d) , in which one of the three corners is directed to the positive direction of the x-axis.
  • This plane shape remains the same at any cross sections disposed in parallel to the above surface regardless of the z-values.
  • the second embodiment differs from the third embodiment as follows.
  • the hole 45 in the second embodiment has a shape such that the aforementioned one corner moves toward the base side of the equilateral triangle as advancing from the side opposite of the active layer 23 to the other side facing the active layer 23 (or to the negative direction of z).
  • the equilateral triangle moves to the positive direction of x as a cross section disposed in parallel to the x-y plane moves to the positive direction of z.
  • the hole 45 has a shape whose upper portion is tilted to the positive direction of x.
  • the hole 55 in the third embodiment has a shape such that the aforementioned one corner moves away from the base of the equilateral triangle as advancing from the side opposite of the active layer 23 to other side facing the active layer 23.
  • the equilateral triangle moves to the negative direction of x as a cross section disposed in parallel to the x-y plane moves to the positive direction of z.
  • the hole 55 has a shape whose upper portion is tilted to the negative direction of x.
  • the Q ⁇ A value and the Q ⁇ B value have been calculated by a three-dimensional FDTD method when a tilted angle 0 is 30 degrees and a filling factor is 16%.
  • the Q ⁇ A value was 4095 and the Q ⁇ B value was 2581 in the second embodiment, whereas the Q ⁇ A value was 5849 and the Q ⁇ B value was 26200 in the third embodiment.
  • the Q ⁇ B value can be suppressed to be lower than the Q ⁇ A value in the second embodiment but the Q ⁇ B value is higher than the Q ⁇ A value in the third embodiment (though the Q ⁇ B value can be made smaller by one to two digits than that of Patent Document 2). Therefore, for a selective laser oscillation by the band edge A, the structure of the second embodiment is more desirable than that of the third embodiment.
  • a laser light source i.e. first comparative example
  • a two-dimensional photonic crystal in which a triangular prism hole 65 whose main axis is disposed in parallel to the z-axis and not tilted to the surface of the matrix body as shown in Fig. 8(a) is arranged in a square lattice pattern.
  • both band edges "A" and "B” have Ey which becomes zero in a node 67 extending in the y-direction in any of the first to third embodiments and the first comparative example.
  • the Q value tends to become smaller as this node 67 is positioned away from the center of gravity of a cross section of the hole in the plane 61.
  • the node 67 is positioned away from the center of gravity (or center of circle) of the hole 25 in the plane 61 in the band edge "B” in comparison with the band edge "A", where the Q ⁇ B value is smaller than the Q ⁇ A value.
  • the distance between the center of gravity 68 and the node 67 in the plane 61 of the hole is longer in the second embodiment than the third embodiment, where the Q ⁇ B value of the third embodiment is smaller than the Q ⁇ B value of the second embodiment. It is likely that the difference between the second embodiment and the third embodiment is brought by x-direction symmetry which is made smaller because the node 67 is displaced to a direction of narrowing a width of the y-direction of the hole (or positive direction of x) in the second embodiment, in addition to the effects of the distance between the center of gravity 68 and the node 67.
  • this node 67 is created in a position close to the volume center an entire hole (i.e. the center of gravity of an entire hole) within the x-y plane, it can be said that the difference in the Q ⁇ B value between the second embodiment and the third embodiment is associated with the difference of the holes in the main axis direction.
  • Figs. 13 to 19 are used to explain an example of the second aspect of the surface-emitting laser.
  • Fig 13 is a perspective view showing a laser light source of the present embodiment.
  • This laser light source has a structure similar to that of the laser light source of the first embodiment except for a two-dimensional photonic crystal layer 74.
  • the structure of the two-dimensional photonic crystal layer 74 is now explained.
  • Fig. 14(a) is a top view of the two-dimensional photonic crystal layer 74.
  • the two-dimensional photonic crystal layer 74 is created from a slab-shaped matrix body made of p-type GaAs with a thickness of 130 nm in which modified refractive index region groups 75 are arranged in a square lattice pattern with a period of 285 nm.
  • Figs. 14(b) and 14(c) are a top view and a longitudinal sectional view of one of the modified refractive index region groups 75, respectively.
  • the modified refractive index region group 75 includes a first hole 751 and a second hole 752 which are created by perforating the matrix body.
  • the first hole 751 has a rectangular shape with a long side of 167 nm, a short side of 87 nm, and a thickness of 120 nm, whereas the second hole 752 has a columnar shape with a diameter of 56 nm and a thickness of 60 nm.
  • the second hole 752 is arranged adjacent to the long side of the first hole. A distance between their centers is 90 nm.
  • a ratio (or filling factor) of the volume occupied by the first hole 751 and the second hole 752 in the two-dimensional photonic crystal layer 74 is 0.18.
  • a method to manufacture the laser light source of the present embodiment is explained referring to Fig. 15 .
  • a first laminate 82 is created by laminating a cladding layer 272, a spacer 262, an active layer 23, and a matrix body 81 made of p-type GaAs in this order using a normal MOCVD method or similar method ( Fig. 15(a) ).
  • a resist 83 is created on the matrix body 81, where a hole 841 of a rectangular plane shape with a long side of 167 nm and a short side of 87 nm and a hole 842 of a circular plane shape with a diameter of 56 nm are created in the resist 83 by a process such as an electron beam exposure process and a nano-imprinting process so as to correspond to positions in which the first hole 751 and the second hole 752 are arranged. Thereafter, an etching gas containing chlorine is introduced on the resist 83 ( Fig. 15(c) ). The matrix body 81 is dry-etched by the etching gas through the rectangular hole 841 and the circular hole 842 respectively.
  • This dry etching is carried out for a predetermined period of time in order to create the first hole 751 having a predetermined thickness under the rectangular hole 841 and a second hole 752, which is thinner than the first hole 751, under the circular hole 842.
  • the two-dimensional photonic crystal layer 74 is thus fabricated ( Fig. 15(d) ). The reason why the first hole 751 and the second hole 752 are created with different thicknesses is explained later.
  • the aforementioned predetermined period of time is obtained by preliminary experiment. After the dry etching is completed, the resist 83 is removed.
  • a second laminate 85 is created by laminating a spacer layer 261, a cladding layer 271, and a contact layer 28 in this order by using a normal MOCVD method or a similar method.
  • the two-dimensional photonic crystal layer 74 is set on the spacer layer 261, and they are fused together by a heating process at temperatures between 200 to 700 degrees Celsius ( Fig. 15(e) ).
  • an anode 21 is deposited onto the surface of the contact layer 28 and the cathode 22 is deposited onto the surface of the cladding layer 272, whereby the laser light source of the present embodiment is completed ( Fig. 15(f) ).
  • first hole 751 and the second hole 751 are created with different thicknesses in the process of Fig. 15(d) is explained. Since the area of the circular hole 842 is sufficiently smaller than the area of the rectangular hole 841 (by about 1/5), it is difficult for an etching gas to penetrate into the circular hole 842 in comparison with the rectangular hole 841. Therefore, the speed of etching to advance from the circular hole 842 is slower than the speed of etching to advance from the rectangular hole 841. Accordingly, an etching depth of the first hole 751 is deeper than that of the second hole 752 when the dry etching is completed, which generates a depth difference between the first hole 751 and the second hole 752.
  • Fig. 16 shows a top view (a) and a longitudinal sectional view (b) of microscopic images of the two-dimensional photonic crystal layer 74 obtained when the last process ( Fig. 15(d) ) of the manufacturing method according to the present embodiment is completed.
  • Fig. 16(a) clearly shows that the first hole 751 of a rectangular plane shape and the second hole 752 of a circular plane shape are created.
  • Fig. 16(b) also suggests that the first hole 751 is thicker than the second hole 752.
  • a relation between a current injected from the electrode and the intensity of light emission was measured in the laser light source of the present embodiment.
  • a similar measurement was also made for a laser light source (i.e. second comparative example) having a structure similar to that of the present embodiment except for a two-dimensional photonic crystal layer created from a matrix body in which columnar holes with a diameter of 110 nm and a height of 100 nm are arranged in a square lattice pattern with a period of 285 nm.
  • Fig. 17(a) shows the measurement result of the present embodiment
  • Fig. 17(b) shows the measurement result of the second comparative example. Higher slope efficiency and stronger intensity of light emission can be obtained in the present embodiment than the second comparative example.
  • Fig. 18 shows the calculation result. In Fig. 18 , the direction of the arrows indicates a direction of an electric field, the length of arrows indicates the intensity of an electric field, and the shading indicates the intensity of a magnetic field.
  • the calculation results shown here are obtained when a distance between the first hole 751 and the second hole 752 is 114 nm ( Fig.
  • Plane shapes of the first hole 751 and the second hole 752 are not limited to the aforementioned shapes.
  • both the first hole 751 and the second hole 752 may have various shapes as shown in Fig. 19 as long as a condition is satisfied in such that the first hole 751 is thicker than the second hole 752 (or the first hole 751 has a larger plane shape than the second hole 752 when the manufacturing method shown in Fig. 15 is used).

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  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
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  • Semiconductor Lasers (AREA)
  • Optical Integrated Circuits (AREA)
  • Lasers (AREA)
EP06783175A 2005-09-05 2006-09-05 Source de lumière laser émettant de la lumière à la surface d'un cristal photonique bidimensionnel Withdrawn EP1933431A4 (fr)

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CN103825196A (zh) * 2014-03-11 2014-05-28 青岛大学 一种二维硅基光子晶体微纳波导激光器
EP2544320A4 (fr) * 2010-03-01 2017-11-29 Japan Science and Technology Agency Laser à cristal photonique
US10461502B2 (en) 2016-02-29 2019-10-29 Kyoto University Two-dimensional photonic crystal surface emitting laser and method of manufacturing the same

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US11309687B2 (en) * 2017-12-08 2022-04-19 Hamamatsu Photonics K.K. Light-emitting device and production method for same
WO2019111787A1 (fr) 2017-12-08 2019-06-13 浜松ホトニクス株式会社 Dispositif électroluminescent et son procédé de production
WO2020045453A1 (fr) * 2018-08-27 2020-03-05 浜松ホトニクス株式会社 Dispositif d'émission de lumière
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EP2544320A4 (fr) * 2010-03-01 2017-11-29 Japan Science and Technology Agency Laser à cristal photonique
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US20090135869A1 (en) 2009-05-28
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US8711895B2 (en) 2014-04-29
EP1933431A4 (fr) 2011-06-15

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